Resinous materials, such as thermoplastic olefins (TPO), sheet molding compounds (SMC), engineering polymers, such as Noryl GTX® polyamide (PA) reinforced with a modified polyphenylene ether polymer (PPE) supplied by GE Company, and reaction injection molded (RIM) polyurethane are used in many applications, such as automobile parts and accessories, containers, household appliances and other commercial items. It is often desirable to coat articles made from such resinous materials with coatings that are esthetically pleasing. Such coatings are also used to protect such articles from degradation when exposed to atmospheric weathering conditions, such as sunlight, moisture, heat and cold. To produce longer lasting and more durable articles from resinous materials, it is necessary for the coatings to tightly adhere to the surface of such articles.
Resinous substrates made from a variety of thermoplastic and thermosetting resinous materials have widely varying surface properties, including surface tension, roughness, flexibility, and have widely varying bulk properties such as solubility parameter, which make it difficult to achieve adequate adhesion of the coatings to such materials, particularly upon aging or environmental exposure of the resinous materials. It is well known to apply an adhesion promoter or tie coat on a resinous substrate surface to improve adherence of the coating to the surface. The application of an adhesion promoter or tie coat is normally an added step in the coating process. The adhesion promoter is usually applied in a thin layer, normally about 6.35 micrometers (0.25 mils). Typically, adhesion promoters used on TPO plastic surfaces contain chlorinated polyolefins, some examples of which are described in U.S. Pat. Nos. 4,997,882; 5,319,032 and 5,397,602. Additionally, flame or corona pretreatment steps can be also used to facilitate adequate adhesion of organic coatings to some resinous substrates.
The use of adhesion promoters and/or corona pretreatments in a coating system used to coat resinous substrates, adds complexity and cost to the system. The application of an adhesion promoter usually entails coating the resinous substrate with the promoter, followed by some drying or curing time which increases the time of the entire coating process and will usually necessitate additional workspace. Accordingly, coating compositions which exhibit excellent adhesion directly to resinous materials, such as TPO and Noryl GTX® polyamide without the use of adhesion promoters or tie coats are desirable.
Polyolefin diols have been used in coating compositions to impart adhesion to the resinous substrate without the use of adhesion promoters or tie coats. However, polyolefin diols may be incompatible with the resins and/or crosslinking agents used in some coating compositions. For example, U.S. Pat. No. 6,203,913 discloses an adhesion promoter containing a mixture of one or more conventional crosslinkable film forming resins having crosslinkable groups, such as those from polyesters, and acrylic polymers; one or more conventional crosslinking materials that are capable of reacting with film forming resins, such as aminoplasts and isocyanates; and an adhesion promoting agent, such as polyolefin diol. However, a need still exists to improve compatibility of the adhesion-promoting agent, film forming resins and crosslinking materials in such coating compositions.